The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
Various systems have been used over the years to help measure atmospheric conditions with the goal of predicting weather conditions. One such method is the use of radiosondes, also known as weather balloons. These devices measure temperature humidity and other variables from the ground up to fairly high altitude. Another approach has been to drop parachute the equivalent of radiosondes from in-flight aircraft. Still another approach has involved Global Positioning System (GPS) occultation measurements from low orbiting satellites, such as the Constellation Observing System for Meteorology, Ionosphere and Climate (COSMIC) constellation of six satellites. Yet another approach has been to use GPS or IRIDIUM (c) occultation measurements taken from in-flight aircraft. IRIDIUM refers to the Iridium Satellite LLC of Bethesda Md.
The above approaches have met with varying degrees of success. For example, radiosonde measurements are effective but their use is limited to industrialized countries over land. The infrastructure to routinely launch and monitor them is lacking in many nations, and particularly over seas and oceans, which cover a substantial portion of the Earth's surface. Dropping small parachute packages from airborne aircraft is technically effective, but is costly over time and in some situations may raise environmental issues.
GPS occultation with satellites makes effective measurements only at fairly high altitudes. The GPS signal is typically too week to effectively traverse the lower atmosphere with sufficient signal quality to allow an occultation measurement. In addition, the spatial and temporal coverage of low Earth orbit (LEO) satellite constellations is too sparse to allow comprehensive coverage.
GPS or Iridium occultation measurements from aircraft provide better coverage than measurements from satellites. Measurements also reach somewhat lower altitudes because the signal does not need to traverse the entire atmosphere twice. However, there is the cost of installing additional antennas and occultation receivers on the aircraft, which in some cases may add significantly to the cost of implementing such a system. Reflected signal occultation is technically better than standard occultation. The reflected signal, especially using Iridium satellites, reaches all the way to the surface, allowing a full profile of the atmosphere to be measured. However, as with standard occultation, this method requires adding special antennas and receivers to the aircraft, and therefore may increase the cost of implementing such a system.